SIMULTANEOUS ESTIMATION OF THE BIOKINETICS OF AMMONIA AND NITRITE OXIDATION FROM A SINGLE RESPIROMETRIC PROFILE USING A COMPREHENSIVE TWO-STEP NITRIFICATION MODEL

摘要

Single-step nitrification models yield erroneous lumped kinetic parameter estimatesrnfor batch NH_4~+_-N to NO_3~--N oxidation when NO_2~--N to NO_3~--N oxidation is ratelimiting.rnTo facilitate determination of both NH_4~+_-N to NO_2~--N and NO_2~--N to NO_3~--Nrnoxidation kinetics from a single extant respirogram of NH_4~+-N to NO_3~--N oxidation, arnmechanistically based nitrification model was formulated that explicitly considers eachrnoxidation step as a Monod type expression. The developed model incorporated a novelrnconvention for expressing nitrogen species concentrations in terms of their nitrogenousrnoxygen demand (NOD). Stoichiometric coefficients relating nitrogen removal, oxygenrnuptake and biomass synthesis were derived from an electron balanced equation.rnA parameter identifiability analysis of the developed two-step model showed the twosteprnmodel kinetic parameter estimates describing NH_4~+-N to NO_2~--N oxidationrn(q_(max,ns) and K_(S,ns)) were strongly correlated with the kinetic parameter estimatesrndescribing NO_2~--N to NO_3~--N oxidation (q_(max,nb) and K_(S,nb)) when NH_4rn~+-N to NO_2~--N oxidation was the sole rate-limiting step in overall nitrification (NH_4~+-N to NO_3~--Nrnoxidation). However, when the NO_2~--N to NO_3~--N oxidation rate was comparable to orrnlower than the NH_4~+-N to NO_2~--N oxidation rate, correlation between the kineticrnparameter estimates of the two individual steps was greatly reduced. These findingsrndemonstrate that the accurate determination of nitrification kinetics entails anrnidentification of the rate-determining step in overall nitrification before applying eitherrnsingle-step or two-step models to describe batch nitrification respirograms. An optimalrnexperimental design is proposed for quantifying both steps from batch respirogramsrnthat will extend the applicability of the two-step model even when NH_4~+-N to NO_2~--Nrnoxidation alone is rate limiting.